(i) Technical Field
The present invention relates to focal plane shutters and optical apparatuses.
(ii) Related Art
There is known a focal plane shutter using a self-holding type solenoid for driving blades. In addition to the self-holding type solenoid, such a focal plane shutter is equipped with a drive lever, a biasing member, and a set member. The drive lever holds a movable iron piece and drives the blades. The self-holding type solenoid is capable of adsorbing to the movable iron piece by a given attraction force in a non-energized state, and reduces the attraction force in an energized state. The biasing member is provided for biasing the drive lever such that the movable iron piece moves away from the self-holding type solenoid. The set member drives the drive lever to abut the movable iron piece with the self-holding type solenoid. Japanese Patent Unexamined Application Publication No. 2010-152000 discloses the focal plane shutter employing the self-holding type solenoid.
The set member drives the movable iron piece to abut the movable iron piece with the self-holding type solenoid in the non-energized state. After that, the set member recedes from the drive lever. A wait state where the self-holding type solenoid is adsorbed to the movable iron piece is maintained. After a given period elapses from when a release button is pushed, the self-holding type solenoid is energized. This reduces the attraction force of the self-holding type solenoid, whereby the drive lever recedes from the self-holding type solenoid in accordance with the biasing force of the biasing member. This drives the blades. Subsequently, the set member moves the drive lever, and a wait state where the self-holding type solenoid is adsorbed to the movable iron piece is maintained again.
Herein, a state where the self-holding type solenoid is adsorbed to the movable iron piece may be maintained for a long period, while a portion where the movable iron piece of the drive lever and a yoke of the self-holding type solenoid abut each other is attached with a lubricant oil applied in producing the focal plane shutter and impure substances such as dusts or metal powders by generated in driving the focal plane shutter. This tends to fix the movable iron piece of the drive lever and the yoke of the self-holding type solenoid. This may result in variations in the period from when energization of the self-holding type solenoid starts to when the drive lever recedes from the self-holding type solenoid after the release button is pushed again. This may result in variations in the timing of driving the blades.